Field of the Invention
The present invention relates to a processor, a host device, a power saving method of a USB device, and a computer program.
Description of the Related Art
In general, a processor such as a printer or an image reader is connected to a host device such as a personal computer to communicate with each other. The processor executes predetermined processing such as printing or reading of an image according to a command from the host device.
There is a universal serial bus (USB) as one of means for connecting a processor to a host device. In a case where the host device which is a USB host proceeds to a power saving mode reducing the power consumption thereof in a state of being connected by the USB, in the processor which is a USB device, a device side USB interface for USB communication is in a power saving state which is referred to as suspend.
In the related art, there is a technology disclosed in JP 2005-196352 A, as a technology of related art for allowing the USB device to return the USB host to a normal mode from the power saving mode.
In JP 2005-196352 A, it is disclosed that when the USB device returns to the normal mode, a switch which pulls up a data line (D+) of the USB interface is turned on, and thus, the USB host returns to the normal mode.
There is a case where the processor uniquely proceeds to the power saving mode without receiving a command from the host device. That is, there is a case where the processor proceeds to the power saving mode even when the host device is in the normal mode without proceeding to the power saving mode. For example, when a user uses a personal computer which is a host device, a printer which is a processor connected to the personal computer is usually in the power saving mode in a case where the printer is not used for a while.
When the processor proceeds to the power saving mode, energization to a central processing unit (CPU) of a controller controlling the operation of the processor is suppressed.
However, the processor is not capable of uniquely setting a device side USB interface to be in the power saving state. For this reason, in a case where the host device which is connected to the processor by the USB is in the normal mode, the device side USB interface is not in the power saving state, and thus, power is wastefully consumed by the device side USB interface in the processor.
Recently, regulations on standby power, such as European Lot26, become restrictive, and thus, power saving is further required. For this reason, it is necessary to suppress wasteful power consumption in the processor as much as possible.
The technology of JP 2005-196352 A is a technology for returning the host device to the normal mode from the power saving mode, and thus, is not capable of solving a problem which occurs in a case where the host device is in the normal mode.